TV/VCR/Stereo Troubleshooting/VCR erratic sound playback
My Panasonic VCR model no. PV-V4021 has started to play back tapes with gaps in the sound (no audio, but still video). Last time I listened to it, it was fine for a while. Then the sound problem occurred and when I rewound the tape and tried again, there were gaps where it had been fine a few minutes earlier. I got this VCR used, but guess it's around 10 years old.
It could be caused by either tape problems or audio playback hardware problems.
one: If the tape is old it could be losing oxide from the surface of the tape. Or, it might be a loss of magnetism of the audio track caused by storing near magnetic sources. VHS tapes don't last much more than a few years in storage. So, if the tape is old it could be deteriorated.
Since you said it is worse after rewinding and playing some of the old sections that played good during the first time it might be the tape's oxide coming off during the play. If this is so then each time you play the tape more oxide will come off.
Try playing a known good tape to determine if it will play as expected; that will help you decide.
two: if the audio tape head is out of adjustment it can cause this problem. A most common cause is the tension being too tight and causing stretch marks on the tape. You can examine for stretched tape by opening the gate of the cartridge and pull out a section of tape and examine the edges of the tape for what looks like wrinkles or edge waving along either side of the tape. If this is the problem it will increase the stretch each time you play the tape. If you use a known good tape then it could also become damaged while being played.
Or, it could be a poor quality tape that just is not good quality and shows stretching merely due to its poor quality nature.
Finally, if the audio playback head inside the machine has been adjusted wrongly or is covered with gunk it can cause audio dropouts. If you are techno inclined you can open the machine by pulling off the cover and examine the audio head for gunk buildup around the playback side of the head. you can find the head visually; the video head is the big round spinning unit and with the cartridge loaded in the machine the audio head is by the side of the video rotary head.
So, these are my preliminary remarks. Send me back a follow up question if you are still not sure what to do next.
PS: Used but good vhs tape players are often found at thrift stores for $5 - $10. So, it is easy to replace a bad one but the cost of repair is virtually never a good cost/benefit.